Optically clear hot melt processable high refractive index adhesives

ABSTRACT

Adhesive compositions that are optically transparent include a (meth)acrylate-based copolymer having a refractive index of at least 1.48, and particles of a thermoplastic polymer. At least some of the particles have an average particle size that is larger than the wavelength of visible light. The adhesive compositions are prepared by hot melt processing packaged adhesive compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2013/076331, filed Dec. 19, 2013, which claims priority to USProvisional Application No. 61/746643, filed Dec. 28, 2012, thedisclosure of which is incorporated by reference in its/their entiretyherein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to adhesives, specifically toadhesives that are optically clear, hot melt processable and that have ahigh refractive index.

BACKGROUND

Adhesives have been used for a variety of marking, holding, protecting,sealing and masking purposes. Adhesive tapes generally comprise abacking, or substrate, and an adhesive. One type of adhesive, apressure-sensitive-adhesive (PSA) is particularly preferred for manyapplications.

PSAs are well known to one of ordinary skill in the art to possesscertain properties at room temperature including the following: (1)aggressive and permanent tack, (2) adherence with no more than fingerpressure, (3) sufficient ability to hold onto an adherend, and (4)sufficient cohesive strength to be removed cleanly from the adherend.Materials that have been found to function well as PSAs are polymersdesigned and formulated to exhibit the requisite viscoelastic propertiesresulting in a desired balance of tack, peel adhesion, and shearstrength. The most commonly used polymers for preparation of PSAs arenatural rubber, synthetic rubbers (e.g., styrene/butadiene copolymers(SBR) and styrene/isoprene/styrene (SIS) block copolymers), and various(meth)acrylate (e.g., acrylate and methacrylate) copolymers. With theexception of several (meth)acrylates, which are inherently tacky, thesepolymers are typically blended with appropriate tackifying resins torender them pressure-sensitive.

Among the advances that have been made in the adhesive area are adhesivethat are prepared in packages or pouches, and adhesives with highrefractive indices. Adhesives have been prepared in packages and pouchesas described for example in U.S. Pat. Nos. 6,294,249 and 6,928,794(Hamer et al.). Additionally, pressure sensitive adhesives with highrefractive indices are described in U.S. Pat. No. 7,335,425 (Olson etal.).

SUMMARY

Disclosed herein are adhesive compositions, packaged adhesivecompositions, articles and methods of preparing articles. Adhesivecompositions of this disclosure are optically transparent and comprise a(meth)acrylate-based copolymer having a refractive index of at least1.48, and particles of a thermoplastic polymer. At least some of theparticles have an average particle size that is larger than thewavelength of visible light.

Also disclosed are packaged adhesive compositions comprising apolymerized pre-adhesive mixture, wherein the polymerizable pre-adhesivecomposition and a packaging material. The polymerizable pre-adhesivecomposition comprises an aromatic monomer in an amount of at least 5parts per 100 parts of total monomer, the aromatic monomer having theformula:

wherein Ar is an aromatic group which is unsubstituted or substitutedwith a substituent selected from the group consisting of Br_(y) and(R³)_(z) wherein y represents the number of bromine substituentsattached to the aromatic group and is an integer from 0 to 3, R³ is astraight or branched alkyl of 2 to 12 carbons, and z represents thenumber of R³ substituents attached to the aromatic ring and is aninteger from 0 to 1, provided that both y and z are not zero, X isoxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl, n is 0 to 3, R¹is an unsubstituted straight or branched alkyl linking group of 2 to 12carbons, and R² is either H or CH₃.

Also disclosed are articles comprising a substrate and an adhesivedisposed on at least a portion of the substrate. The adhesive comprisesa (meth)acrylate-based copolymer having a refractive index of at least1.48, particles of a thermoplastic polymer, at least some of theparticles having an average particle size that is larger than thewavelength of visible light, wherein the adhesive composition isoptically transparent.

Also disclosed are methods of preparing adhesive articles comprisingproviding a hot melt processable packaged adhesive composition, hot meltprocessing the packaged adhesive composition, and disposing the hot meltprocessed packaged adhesive composition on a substrate. The packagedadhesives are described above. Providing a hot melt processable packagedadhesive composition comprises combining a polymerizable pre-adhesivereactive mixture and a packaging material to form a packagedpre-adhesive composition, and polymerizing the pre-adhesive mixture. Thepolymerizable pre-adhesive composition is described above.Polymerization of the packaged pre-adhesive composition can be effectedby activation of an initiator present in the pre-adhesive composition,or by exposure to gamma radiation.

DETAILED DESCRIPTION

The use of adhesives, especially pressure sensitive adhesives, in areassuch as the medical, electronic, automotive, and optical industries isincreasing. The requirements of these industries place additionaldemands upon the pressure sensitive adhesive beyond the traditionalproperties of tack, peel adhesion and shear strength. New classes ofmaterials are desirable to meet the increasingly demanding performancerequirements for pressure sensitive adhesives. Among the performancerequirements for new classes of pressure sensitive adhesives are opticalproperties such as being optically transparent or optically clear.

Many classes of pressure sensitive adhesive have been prepared toaddress the increased need for performance issues. Often these pressuresensitive adhesives are provided as solutions or solvent-borne mixtures,often solutions or solvent-borne mixtures containing large amounts ofsolvents. Upon coating or dispensing, the solvent needs to be removed toproduce an adhesive layer. Often the solvent is removed through the useof elevated temperature processing such as heating with an oven. Suchsolvent removal steps can add cost to the formed articles becausesolvent removal requires additional steps. Not only are additional stepsinvolved, often these steps require specialized care, precautions andequipment because the solvents are volatile and generally flammable. Inaddition, shipment of adhesive solutions adds additional expense becauseof the added weight of solvent and may require special shipmentprecautions due to the presence of solvent. Environmental concerns arealso an issue with solvent borne adhesive systems, since, even with theuse of solvent reclamation equipment, solvent release to the environmentis likely.

Therefore, 100% solids adhesive systems have been developed. Among these100% solids systems are hot melt processable adhesives, including hotmelt processable pressure sensitive adhesives. Difficulties have arisenwhen solvent processing has been replaced by hot melt processing. Oftenit is difficult to replicate the properties of solvent deliveredadhesive layers with hot melt delivered systems.

Additionally, because 100% solids pressure sensitive adhesives are tackypolymeric compositions, handling of these compositions, especially on alarge scale can be problematic. A wide variety of techniques have beendeveloped to deal with these handling issues. One such technique is thepreparation of pressure sensitive adhesive polymers or compositionswithin a polymeric pouch. These pouches can then be handled withoutcontacting the tacky polymeric composition. The entire pouch can then behot melt processed, for example in an extruder or similar mixing device,and coated to form a pressure sensitive adhesive layer. This layercontains not only the pressure sensitive adhesive polymer orcomposition, but also the remnants of the pouch material. Often theremnants of the pouch material comprise polymeric particles. In systemswhere the pressure sensitive adhesive is not visible (such as with manytape constructions) or where the pressure sensitive adhesive need nothave optical properties, the presence of polymeric particles istypically not an issue. However, if the particles are large enough toscatter visible light, that is to say larger than the wavelengths oflight associated with the visible portion of the spectrum, and thepolymeric particles are of a different refractive index than thepressure sensitive adhesive polymer or composition, the adhesive layercan scatter visible light. This scattering has the detrimental result ofdecreased visible light transmission and increased haze. The need foradhesive layers with increasingly demanding optical properties, such ashigh visible light transmission and low haze, makes the desirableprocess of preparing of pressure sensitive adhesive polymers orcompositions within a polymeric pouch and then hot melt processing andcoating these pouches to form an adhesive layer, appear to be unlikelyto succeed.

Disclosed herein are adhesive compositions and techniques developed topermit the use of the desirable preparation of pressure sensitiveadhesive polymers or compositions within a polymeric pouch and then hotmelt processing and coating these pouches to form an adhesive layer toproduce adhesive layers with desirable optical properties, such as highvisible light transmission and/or low haze. These pressure sensitiveadhesive compositions comprise (meth)acrylate-based polymers with arelatively high refractive index. These relatively high refractivepolymers are higher than conventional (meth)acrylate-based polymers usedin pressure sensitive adhesives, and are designed to be similar to therefractive index of the polymers used in the pouch materials. Thus, evenif the remnants of the pouches are present as particles that are largerthan the wavelength of visible light, the limitation of the mismatch ofrefractive indices between the (meth)acrylate based polymer and thepouch remnant particles permits the generation of adhesive layers withdesirable optical properties, such as high visible light transmissionand/or low haze.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The recitation of numerical ranges byendpoints includes all numbers subsumed within that range (e.g. 1 to 5includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within thatrange.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. For example,reference to “a layer” encompasses embodiments having one, two or morelayers. As used in this specification and the appended claims, the term“or” is generally employed in its sense including “and/or” unless thecontent clearly dictates otherwise.

The term “adhesive” as used herein refers to polymeric compositionsuseful to adhere together two adherends. Examples of adhesives are heatactivated adhesives and pressure sensitive adhesives.

Heat activated adhesives are non-tacky at room temperature but becometacky and capable of bonding to a substrate at elevated temperatures.These adhesives usually have a T_(g) (glass transition temperature) ormelting point (T_(m)) above room temperature. When the temperature iselevated above the T_(g) or T_(m), the storage modulus usually decreasesand the adhesive becomes tacky.

Pressure sensitive adhesive compositions are well known to those ofordinary skill in the art to possess properties including the following:(1) aggressive and permanent tack, (2) adherence with no more thanfinger pressure, (3) sufficient ability to hold onto an adherend, and(4) sufficient cohesive strength to be cleanly removable from theadherend. Materials that have been found to function well as pressuresensitive adhesives are polymers designed and formulated to exhibit therequisite viscoelastic properties resulting in a desired balance oftack, peel adhesion, and shear holding power. Obtaining the properbalance of properties is not a simple process.

The terms “glass transition temperature” and “T_(g)” are usedinterchangeably. Typically T_(g) values are measure using DifferentialScanning calorimetry (DSC) unless otherwise noted.

The term “room temperature” refers to ambient temperature, generally20-22° C., unless otherwise noted.

The term “(meth)acrylate” refers to monomeric acrylic or methacrylicesters of alcohols. Acrylate and methacrylate monomers or oligomers arereferred to collectively herein as “(meth)acrylates”. Polymers describedas “(meth)acrylate-based” are polymers or copolymers prepared primarily(greater than 50% by weight) from (meth)acrylate monomers and mayinclude additional ethylenically unsaturated monomers.

Unless otherwise indicated, “optically transparent” refers to anarticle, film or adhesive composition that has a high lighttransmittance over at least a portion of the visible light spectrum(about 400 to about 700 nm).

Unless otherwise indicated, “optically clear” refers to an adhesive orarticle that has a high light transmittance over at least a portion ofthe visible light spectrum (about 400 to about 700 nm), and thatexhibits low haze.

The term “wavelength of visible light” as used herein encompasses thewavelengths of the light spectrum that constitutes visible light (about400 to about 700 nm).

Refractive index is defined herein as the absolute refractive index of amaterial (e.g., a monomer or the polymerized product thereof) which isunderstood to be the ratio of the speed of electromagnetic radiation infree space to the speed of the radiation in that material, with theradiation being of sodium yellow light at a wavelength of about 583.9nanometers (nm). The refractive index can be measured using knownmethods and is generally measured using an Abbe Refractometer.

The term “adjacent” as used herein when referring to two layers meansthat the two layers are in proximity with one another with nointervening open space between them. They may be in direct contact withone another (e.g. laminated together) or there may be interveninglayers.

The term “alkyl” refers to a monovalent group that is a radical of analkane, which is a saturated hydrocarbon. The alkyl can be linear,branched, cyclic, or combinations thereof and typically has 1 to 20carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl,n-heptyl, n-octyl, and ethylhexyl.

The term “aryl” refers to a monovalent group that is aromatic andcarbocyclic. The aryl can have one to five rings that are connected toor fused to the aromatic ring. The other ring structures can bearomatic, non-aromatic, or combinations thereof. Examples of aryl groupsinclude, but are not limited to, phenyl, biphenyl, terphenyl, anthryl,naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl,pyrenyl, perylenyl, and fluorenyl.

The term “alkylene” refers to a divalent group that is a radical of analkane. The alkylene can be straight-chained, branched, cyclic, orcombinations thereof. The alkylene often has 1 to 20 carbon atoms. Insome embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylenecan be on the same carbon atom (i.e., an alkylidene) or on differentcarbon atoms.

The term “arylene” refers to a divalent group that is carbocyclic andaromatic. The group has one to five rings that are connected, fused, orcombinations thereof. The other rings can be aromatic, non-aromatic, orcombinations thereof. In some embodiments, the arylene group has up to 5rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromaticring. For example, the arylene group can be phenylene.

The terms “free radically polymerizable” and “ethylenically unsaturated”are used interchangeably and refer to a reactive group which contains acarbon-carbon double bond which is able to be polymerized via a freeradical polymerization mechanism.

Disclosed herein are adhesive compositions that are opticallytransparent and comprise a (meth)acrylate-based copolymer having arefractive index of at least 1.48, particles of a thermoplastic polymer,at least some of the particles having an average particle size that islarger than the wavelength of visible light. The adhesive compositionmay also contain other optional additives. These optically transparentcompositions typically have a visible light transmission of greater than85%. In some embodiments that optically transparent compositions have avisible light transmission of greater than 90%. In addition, theseoptically transparent compositions typically have a haze value of lessthan 10%, and in some embodiments less than 5%.

In some embodiments of this disclosure, the adhesive composition isoptically clear. Optically clear compositions generally have visiblelight transmission of greater than 90%, and a haze of less than 5%. Insome embodiments, the optically clear compositions may have a visiblelight transmission of greater than 95% and/or a haze value of less than2%.

Visible light transmission and haze can be measured using wellunderstood optical techniques. For example, visible light transmissionand haze can be measured with a BYK Gardner Spectrophotometer using thetechniques described in the test method ASTM D1003. The opticalproperties of the adhesive composition, such as whether the adhesivecomposition is optically transparent or optically clear, can depend onwide variety of parameters. Among these parameters are: the compositionof the (meth)acrylate-based polymer; the composition of the particles;the presence or absence of optional additives; the processing conditionsused to prepare the adhesive composition; and so forth. The desiredoptically properties can be different for different applications andintended uses, and thus, a variety of different adhesive compositionswith different optical properties can be suitable. For example, for someapplications, optically transparent adhesive compositions are suitable,whereas for other applications, optically clear adhesive compositionsare necessary.

The (meth)acrylate-based copolymer having a refractive index of at least1.48 is prepared from a variety of (meth)acrylate monomers, and may alsocontain other free radically polymerizable monomers. In someembodiments, the refractive index of the (meth)acrylate-based copolymeris at least 1.50. The refractive index of the (meth)acrylate-basedcopolymer is one of the parameters used to control the final propertiesof the adhesive compositions of this disclosure and therefore a varietyof refractive indices of at least 1.48 are included in this disclosure.

At least one of the monomers in the (meth)acrylate-based copolymer is anaromatic monomer with a relatively high refractive index. Typically thearomatic monomer has a homopolymer glass transition temperature (T_(g))at or below 70° C., or even at or below 50° C. In this disclosure, the(meth)acrylate-based copolymer typically comprises at least one aromaticmonomer in an amount of at least 5 parts by weight per 100 parts byweight of total monomer. In some embodiments, the (meth)acrylate-basedcopolymer typically comprises at least one aromatic monomer in an amountof at least 10 parts by weight per 100 parts by weight of total monomer,at least 15 parts by weight per 100 parts by weight of total monomer, atleast 20 parts by weight per 100 parts by weight of total monomer, atleast 25 parts by weight per 100 parts by weight of total monomer, oreven at least 30 parts by weight per 100 parts by weight of totalmonomer. Because these monomers tend to be more expensive than typical(meth)acrylate monomers and because they typically have a higher T_(g)than typical (meth)acrylate monomers used in preparing adhesives such aspressure sensitive adhesives, it is often desirable to limit the amountof aromatic monomer present in the (meth)acrylate-based polymer.

The level of aromatic monomer and the identity of the particulararomatic monomer or monomers used depends at least in part upon thedesired properties of the (meth)acrylate-based copolymer. Because thearomatic monomers tend to have higher homopolymer glass transitiontemperatures than conventional (meth)acrylate monomers used in thepreparation of adhesive polymers, some care should be exercized in thechoice and amount of aromatic monomers used in the preparation of the(meth)acrylate-based copolymer. If the (meth)acrylate-based copolymer isto have pressure sensitive adhesive properties, typically pressuresensitive adhesive copolymers have a glass transition temperature of 20°C. or less, more typically 0° C. or less. If however, the(meth)acrylate-based copolymer is to have heat activated adhesiveproperties, the copolymers can have a higher glass transitiontemperature.

Examples of suitable aromatic monomers include those described in U.S.Pat. No. 7,335,425 (Olson et al.) and can be described by the generalFormula 1 below:

wherein

-   Ar is an aromatic group which is unsubstituted or substituted with a    substituent selected from the group consisting of Br_(y) and    (R³)_(z), wherein y represents the number of bromine substituents    attached to the aromatic group and is an integer from 0 to 3, and R³    is a straight or branched alkyl of 2 to 12 carbons, and z represents    the number of R³ substituents attached to the aromatic ring and is    an integer from 0 to 1, provided that both y and z are not zero;-   X is oxygen, sulfur or —NR⁴—, wherein R⁴ is H or a C₁-C₄ alkyl; n is    0 to 3;-   R¹ is an unsubstituted straight or branched alkyl linking group of 2    to 12 carbons; and R² is either H or CH₃.

In some embodiments of aromatic monomers, X is oxygen. Within thisembodiment

of aromatic monomers, a group of monomers includes those of Formula 2wherein Ar is naphthyl:

and R¹, R², and n are as defined above. The naphthyl group isunsubstituted or substituted as described above. Within the group ofnaphthyl aromatic monomers, another group are those wherein Ar is1-napthyl or 2-napthyl.

Within the embodiment of aromatic monomers where X is oxygen, anothergroup of monomers includes those of Formula 3 wherein Ar is phenyl:

and R¹, R², and n are as defined above. The phenyl group isunsubstituted or substituted as described above. Within the substitutedgroup of phenyl aromatic monomers, generally the phenyl is dibromosubstituted. Within the bromine substituted group, the phenyl monomersmay also be 2-alkyl substituted or 4-alkyl substituted.

In other embodiments of aromatic monomers, X is sulfur. Within thisembodiment of aromatic monomers, a group of monomers includes those ofFormula 4 wherein Ar is naphthyl:

and R¹, R², and n are as defined above. The naphthyl group isunsubstituted or substituted as described above. Within the group ofnaphthyl aromatic monomers, an additional group is that wherein Ar is1-napthyl or 2-napthyl.

Within the embodiment of aromatic monomers where X is sulfur, anothergroup of monomers includes those of Formula 5 wherein Ar is phenyl:

and R¹, R², and n are as defined above. The phenyl group isunsubstituted or substituted as described above. Within this group ofphenyl aromatic monomers, generally the phenyl is dibromo substituted.In another group, the phenyl monomers may be 2-alkyl substituted or4-alkyl substituted.

Some specific examples of such aromatic monomers suitable in the presentdisclosure include, but are not limited to, 6-(4,6-dibromo-2-isopropylphenoxy)-1-hexyl acrylate, 6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexylacrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecylphenyl acrylate, 2-(1-naphthyloxy)-1-ethyl acrylate,2-(2-naphthyloxy)-1-ethyl acrylate, 6-(1-naphthyloxy)-1-hexyl acrylate,6-(2-naphthyloxy)-1-hexyl acrylate, 8-(1-naphthyloxy)-1-octyl acrylate,8-(2-naphthyloxy)-1-octyl acrylate, 2-phenylthio-1-ethyl acrylate, andphenoxy ethyl acrylate.

One particularly suitable class of aromatic monomers are those describedin US Patent Publication No. 2010/0048804 (Determan et al.). Thesearomatic monomers are represented by the general Formula 6 below:

wherein

-   X¹ and X² are each independently —O—, —S—, or —NR⁴—, wherein R⁴ is H    or C₁-C₄ alkyl, in some embodiments, X¹ and X² are each —O—;-   R¹ is an alkylene of 1 to 8 carbons, and may contain one or more    ether oxygen atoms and one or more pendent hydroxy groups;-   n is integer of from 0 to 3; and-   R² is either H or CH₃.

In certain embodiments of the aromatic monomer of Formula 6, R¹ is analkylene of 1 to 8 carbons; i.e. —C_(a)H_(2a)—, where a is 1 to 8. Inother embodiments R¹ may contain one or more catenary ether oxygenatoms; e.g. —C_(b)H_(2b)—O—C_(c)H_(2c)—, where b and c are at least 1and b+c is 2 to 8. In another embodiment R¹ may contain a pendenthydroxy group; e.g. —C_(b)H_(2b)—CH(OH)—C_(c)H_(2c)—, where b and c areat least 1 and b+c is 2 to 8. If desired, the biphenyl group may bebrominated to increase the refractive index of the resulting adhesive.However such bromine substitution may also increase the Tg of theadhesive. The biphenyl ring may have zero to two bromine atoms, and aretypically substituted ortho- and/or para- to the X¹ group. Particularlydesirable biphenyl monomers are those that have homopolymer glasstransition temperatures at or below 70° C.

A wide variety of co-monomers can be used together with the aromaticmonomers described above to generate the desired (meth)acrylate-basedcopolymer. These co-monomers include alkyl(meth)acrylate monomers, polar(meth)acrylate and ethylenically unsaturated monomers, and otherethylenically unsaturated monomers.

Useful alkyl(meth)acrylate monomers may be present at ranges up to 95parts by weight per 100 parts by weight total monomer. More typicallythe alkyl(meth)acrylate are present at a level of 70-95 parts by weightper 100 parts by weight total monomers. Useful monomers include at leastone monomer selected from the group consisting of a monomeric acrylic ormethacrylic acid ester of a non-tertiary alkyl alcohol, the alkyl groupof which comprises from about 1 to about 12 carbon atoms, more typicallyfrom about 4 to about 8 carbon atoms, and mixtures thereof.

Suitable alkyl(meth)acrylate monomers include, but are not limited to,those selected from the group consisting of the esters of acrylic acidor methacrylic acid with non-tertiary alkyl alcohols such as 1-butanol,1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol,1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol,1-dodecanol, and the like, and mixtures thereof. Such monomeric acrylicor methacrylic esters are known in the art and are commerciallyavailable.

Additionally, the (meth)acrylate-based copolymer may also containcopolymerizable polar monomers. Polar monomers can be used to increasethe cohesive strength of the adhesive. Generally, polar monomers aretypically present at ranges from about 0 to about 12 parts by weight per100 parts by weight total monomer, more typically from about 2 to about8 parts by weight per 100 parts by weight total monomer. Useful polarmonomers include, but are not limited to, those selected from the groupconsisting of ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, and ethylenically unsaturated phosphoricacids, and mixtures thereof. Examples of such compounds include, but arenot limited to, those selected from the group consisting of acrylicacid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid,citraconic acid, maleic acid, B-carboxyethyl acrylate, sulfoethylmethacrylate, and the like, and mixtures thereof.

Other useful copolymerizable polar monomers include, but are not limitedto, acrylamides, N,N-dialkyl substituted acrylamides, N-vinyl lactams,and N,N-dialkylaminoalkyl acrylates, and mixtures thereof. Illustrativeexamples include, but are not limited to, those selected from the groupconsisting of N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide,N,N-diethyl acrylamide, N,N-diethyl methacrylamide,N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylmethacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylacrylate, and the like, and mixtures thereof.

Particularly useful polar monomers include acrylic acid, methacrylicacid, itaconic acid, acrylamide, methacrylamide, acrylonitrile,methacrylonitrile, and mixtures thereof.

Other ethylenically unsaturated monomers, such as vinyl monomers, may beadded to improve performance, reduce cost, etc. in quantities which donot adversely affect the desired optical or adhesive properties of theadhesive. When used, vinyl monomers useful in the adhesive copolymerinclude vinyl esters (e.g., vinyl acetate and vinyl propionate),styrene, substituted styrene (e.g., α-methyl styrene), and mixturesthereof. If used, such vinyl monomers are generally used at 0 to 5 partsby weight, more typically 1 to 5 parts by weight, based on 100 parts byweight total monomer.

In order to increase cohesive strength of the (meth)acrylate-basedcopolymer, it may be crosslinked. Because the (meth)acrylate-basedcopolymer is typically hot melt processed, crosslinking is generallycarried out after hot melt processing with crosslinking agents that arenot affected by hot melt processing. Typically, such crosslinkers areused in amounts of about 0.05 to 1.0 parts by weight of crosslinker per100 parts by weight of total monomers present in the(meth)acrylate-based copolymer.

Typically, the crosslinker is a chemical crosslinker that generates freeradicals to affect the crosslinking reaction. One suitable class ofchemical crosslinkers is a photosensitive crosslinker which is activatedby high intensity ultraviolet (UV) light. Two common photosensitivecrosslinkers used for (meth)acrylate-based copolymers are benzophenoneand copolymerizable aromatic ketone monomers as described in U.S. Pat.No. 4,737,559. Another photocrosslinker, which can be blended with the(meth)acrylate-based copolymer and activated by UV light is a triazine,for example, 2,4-bis(trichloromethyl)-6-(4-methoxy-phenyl)-s-triazine.These crosslinkers are activated by UV light generated from artificialsources such as medium pressure mercury lamps or a UV blacklight.

Additionally, crosslinking can be effected on (meth)acrylate-basedcopolymers after hot melt processing without the addition or presence ofa crosslinking agent through the exposure of the polymer to high energyelectromagnetic radiation such as gamma radiation or by exposure to ane-beam (electron beam).

Alternatively, crosslinking can be effected through thermally reversiblephysical crosslinks that result, for example, from the formation ofreinforcing domains due to phase separation of hard segments (i.e.,those having a Tg higher than room temperature, preferably higher than70° C.) and/or acid/base interactions (i.e., those involving functionalgroups within the same polymer or between polymers or between a polymerand an additive).

The adhesive composition also comprises particles of a thermoplasticpolymer, at least some of the particles having an average particle sizethat is larger than the wavelength of visible light. As will bediscussed in greater detail below, the particles are the remnant ofpouches prepared from thermoplastic films and hot melt processing.

Suitable thermoplastic materials include polyethylene, and ethylenecopolymers such as ethylene/polyolefin copolymers and ethylene/vinylcopolymers such as ethylene vinyl acetate (EVA), ethylene methylacrylate (EMA), ethylene acrylic acid (EAA), EAA ionomers, andpolypropylene, and other thermoplastic materials such as acrylics,polyphenylene ether, polyphenylene sulfide,acrylonitrile-butadiene-styrene copolymer (ABS), polyurethanes, andothers know to those skilled in the art. Blends of thermoplasticmaterials may also be used. Particularly suitable thermoplasticmaterials are polyethylene and EVA.

The particles may be of a wide range of sizes and shapes, as long as atleast some particles have an average particle size that is larger thanthe wavelength of visible light. Because the particles are formed fromthe hot melt processing of a pouches that have been prepared from films,the sizes, shapes, as well as the range of sizes and shapes can belargely dependent upon the hot melt processing conditions. This will bediscussed in greater detail below.

In some embodiments, at least some of the particles are relativelylarge. The particles can have a variety of shapes, but typically theyare longer in one dimension and narrower in the other two dimensions,roughly needle-shaped. In some embodiments, the particles may be 1micrometer or even longer in the longest dimension. In some embodiments,the particles may be up to 5 micrometers in the longest dimension.Various techniques can be used to determine the dimensions of theparticles such as electron microscopy or optical microscopy. As shown inthe Examples section below, optical microscopy was used to determineparticle size.

The adhesive composition may also include a variety of optionaladditives as long as the additives do not interfere with the desiredoptical and adhesive properties of the adhesive composition. Examples ofsuitable additives include tackifiers, plasticizers, and otherperformance enhancement additives. Additionally, for opticalapplications, tackifiers, plastizicers and other additives should havelow color; i.e. a Gardner value of greater than 3, more typicallygreater than 1.

Examples of useful tackifiers include, but are not limited to, rosin,rosin derivatives, polyterpene resins, coumarone-indene resins, and thelike. Plasticizers which may be added to the adhesive may be selectedfrom a wide variety of commercially available materials.

Representative plasticizers include polyoxyethylene aryl ether, dialkyladipate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenylphosphate, di-(2-ethylhexyl) adipate, toluenesulfonamide, dipropyleneglycol dibenzoate, polyethylene glycol dibenzoate, polyoxypropylene arylether, dibutoxyethoxyethyl formal, and dibutoxyethoxyethyl adipate. Whenused, tackifiers are preferably added in an amount not to exceed about50 parts by weight per 100 parts by weight copolymer, and plasticizermay be added in an amount up to about 50 parts by weight per 100 partsby weight copolymer.

It is desirable that any added tackifier and/or plasticizer has arefractive index of at least 1.50, so that incorporation does not reducethe refractive index of the adhesive. Useful high refractive indexplasticizers include aromatic phosphate esters, phtalates, benzoicethers, aromatic sulfonamide, and some rosins. The phosphate esters andphtalates are preferred. Exemplery plasticizer include diethylene glycoldibenzoate (1.5424 n25/D), 4-(tert-butyl)phenyl diphenyl phosphate(1.555 n25/D), trimethylphenyl phosphate (1.5545 n25/D), triphenylphosphate (1.5575 n25/D), phenylmethyl benzoate (1.56 n25/D), diethyleneglycol dibenzoate (1.5424 n25/D), butyl benzyl phthalate (1.537 n25/D),methyl ester of rosin (1.531 n20/D), alkyl benzyl phthalate (1.526n25/D), butyl(phenylsulfonyl)amine (1.525 n20/D), benzyl phthalate(1.518 n25/D), trimethyl trimellitate (1.523 (n20/D), and 2-ethylhexyldiphenyl phosphate (1.51 (n20/D).

Other additives can be added in order to enhance the performance of theadhesive compositions. Examples of such performance enhancing additivesinclude leveling agents, ultraviolet light absorbers, hindered aminelight stabilizers (HALS), oxygen inhibitors, wetting agents, rheologymodifiers, defoamers, biocides, dyes, pigments, and the like. All ofthese additives and the use thereof are well known in the art. It isunderstood that any of these compounds can be used so long as they donot deleteriously affect the adhesive and optical properties.

Among the particularly useful additives are UV absorbers and hinderedamine light stabilizers (HALS). UV absorbers and hindered amine lightstabilizers act to diminish the harmful effects of UV radiation on theadhesive composition and thereby enhance the weatherability, orresistance to cracking, yellowing and delamination of coatings preparedfrom the adhesive compositions. A suitable HALS isbis(1,2,2,6,6-pentamethyl-4-piperidinyl)[3,5-bis(1,1-dimethylethyl-4-hydroxyphenyl)methyl]butylpropanedioate,available as TINUVIN 144, from CIBA-GEIGY Corporation, Hawthorne, N.Y.

The following UV absorbers and combinations thereof in concentrations ofless than 5 parts by weight based on the total monomer composition, mayproduce desirable results, with concentrations in the range of 1-5 partsby weight based on the total monomer composition being particularlysuitable:bis(1,2,2,6,6-pentamethyl-4-piperidinyl)(3,5-bis(1,1-dimethylethyl1-4-hydroxyphenyl)methyl)butylpropanedioate,2-ethylhexyl-2-cyano-3,3′-diphenylacrylate,2-hydroxyl-4-n-octoxybenzophenone,2-(2′-hydroxy-5′-methylphenyl)benzotriazole, poly(oxy-1,2-ethanediyl),alpha-(3-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxylphenyl)-1-oxopropyl)-omega-hydroxy,and UVINUL D-50 and UVINUL MS-40, sold by BASF Wyandotte Inc.,Parsippany, N.J.

Additionally, the adhesive composition may also contain particles, aslong as the particles do not interfere with the desired opticalproperties of the adhesive composition. These particles are deliberatelyadded, and are not those resulting from the hot melt processing of thepouch material. Particularly suitable are particles that do not scattervisible light but absorb light of one wavelength and re-emit the lightat a different wavelength. Examples of such particles include thephosphor particles described in U.S. Pat. No. 7,294,861 (Schardt etal.).

Also disclosed herein are packaged adhesive compositions comprising anadhesive composition and a packaging material. The adhesive compositioncomprises a polymerized pre-adhesive mixture comprising a(meth)acrylate-based copolymer with a refractive index of at least 1.48.The adhesive composition may also comprise a variety of differentadditives.

The adhesive composition is prepared by polymerizing a polymerizablepre-adhesive mixture. The polymerizable pre-adhesive mixture comprisesan aromatic monomer having a relatively high refractive index and mayalso include a mixture of free radically polymerizable comonomers, and apolymerization initiator.

Examples of suitable aromatic monomers include those described in U.S.Pat. No. 7,335,425 (Olson et al.) that have been described above and canbe described by the general Formula 1 below:

wherein

-   Ar is an aromatic group which is unsubstituted or substituted with a    substituent selected from the group consisting of Br_(y) and    (R³)_(z), wherein y represents the number of bromine substituents    attached to the aromatic group and is an integer from 0 to 3, and R³    is a straight or branched alkyl of 2 to 12 carbons, and z represents    the number of R³ substituents attached to the aromatic ring and is    an integer from 0 to 1, provided that both y and z are not zero;-   X is oxygen, sulfur or —NR⁴—, wherein R⁴ is H or a C₁-C₄ alkyl; n is    0 to 3;-   R¹ is an unsubstituted straight or branched alkyl linking group of 2    to 12 carbons; and R² is either H or CH₃.

One particularly suitable class of aromatic monomers are those describedin US Patent Publication No. 2010/0048804 (Determan et al.). Thesearomatic monomers have been described above and are represented by thegeneral Formula 6 below:

wherein

-   X¹ and X² are each independently —O—, —S—, or —NR⁴—, wherein R⁴ is H    or C₁-C₄ alkyl, in some embodiments, X¹ and X² are each —O—;-   R¹ is an alkylene of 1 to 8 carbons, and may contain one or more    ether oxygen atoms and one or more pendent hydroxy groups;-   n is integer of from 0 to 3; and-   R² is either H or CH₃.

In this disclosure, the pre-adhesive mixture typically comprises atleast one aromatic monomer in an amount of at least 5 parts by weightper 100 parts by weight of total monomers. In some embodiments, thepre-adhesive mixture comprises at least one aromatic monomer in anamount of at least 10 parts by weight per 100 parts by weight of totalmonomer, at least 15 parts by weight per 100 parts by weight of totalmonomer, at least 20 parts by weight per 100 parts by weight of totalmonomer, at least 25 parts by weight per 100 parts by weight of totalmonomer, or even at least 30 parts by weight per 100 parts by weight oftotal monomer. Because these monomers tend to be more expensive thantypical (meth)acrylate monomers and because they typically have a higherT_(g) than typical (meth)acrylate monomers used in preparing adhesivessuch as pressure sensitive adhesives, it is often desirable to limit theamount of aromatic monomer present in the (meth)acrylate-based polymer.

The pre-adhesive mixture may also comprise a wide variety of co-monomerstogether with the aromatic monomers described above. These co-monomersinclude alkyl(meth)acrylate monomers, polar (meth)acrylate andethylenically unsaturated monomers, and other ethylenically unsaturatedmonomers.

Useful alkyl(meth)acrylate monomers may be present at ranges up to 95parts by weight per 100 parts by weight total monomer. More typicallythe alkyl(meth)acrylate are present at a level of 70-95 parts by weightper 100 parts by weight total monomers. Useful monomers include at leastone monomer selected from the group consisting of a monomeric acrylic ormethacrylic acid ester of a non-tertiary alkyl alcohol, the alkyl groupof which comprises from about 1 to about 12 carbon atoms, more typicallyfrom about 4 to about 8 carbon atoms, and mixtures thereof.

Suitable alkyl(meth)acrylate monomers include, but are not limited to,those selected from the group consisting of the esters of acrylic acidor methacrylic acid with non-tertiary alkyl alcohols such as 1-butanol,1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol,1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol,1-dodecanol, and the like, and mixtures thereof. Such monomeric acrylicor methacrylic esters are known in the art and are commerciallyavailable.

Additionally, the pre-adhesive mixture may also contain copolymerizablepolar monomers. Polar monomers can be used to increase the cohesivestrength of the adhesive. Generally, polar monomers are typicallypresent at ranges from about 0 to about 12 parts by weight per 100 partsby weight total monomer, more typically from about 2 to about 8 parts byweight per 100 parts by weight total monomer. Useful polar monomersinclude, but are not limited to, those selected from the groupconsisting of ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, and ethylenically unsaturated phosphoricacids, and mixtures thereof. Examples of such compounds include, but arenot limited to, those selected from the group consisting of acrylicacid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid,citraconic acid, maleic acid, B-carboxyethyl acrylate, sulfoethylmethacrylate, and the like, and mixtures thereof.

Other useful copolymerizable polar monomers include, but are not limitedto, acrylamides, N,N-dialkyl substituted acrylamides, N-vinyl lactams,and N,N-dialkylaminoalkyl acrylates, and mixtures thereof. Illustrativeexamples include, but are not limited to, those selected from the groupconsisting of N,N-dimethyl acrylamide, N,N-dimethyl methacrylamide,N,N-diethyl acrylamide, N,N-diethyl methacrylamide,N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylmethacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylacrylate, and the like, and mixtures thereof.

Particularly useful polar monomers include acrylic acid, methacrylicacid, itaconic acid, acrylamide, methacrylamide, acrylonitrile,methacrylonitrile, and mixtures thereof.

Other ethylenically unsaturated monomers, such as vinyl monomers, may beadded to improve performance, reduce cost, etc. in quantities which donot adversely affect the desired optical or adhesive properties of theadhesive. When used, vinyl monomers useful in the adhesive copolymerinclude vinyl esters (e.g., vinyl acetate and vinyl propionate),styrene, substituted styrene (e.g., α-methyl styrene), and mixturesthereof. If used, such vinyl monomers are generally used at 0 to 5 partsby weight, more typically 1 to 5 parts by weight, based on 100 parts byweight total monomer.

Besides the above listed monomers, the pre-adhesive mixture may alsocomprise optional additional additives such as a crosslinker or a chaintransfer agent. In order to increase cohesive strength of the(meth)acrylate-based copolymer, it may be crosslinked. Because thepackaged adhesive composition is typically hot melt processed,crosslinking is generally carried out after hot melt processing withcrosslinking agents that are not affected by hot melt processing.Therefore, crosslinkers in this context refer to materials thatcopolymerize with the (meth)acrylate monomers described above, and thenare subsequently activated to create crosslinks. In this way, thepolymerized packaged adhesive composition is not crosslinked andtherefore is hot melt processable, but upon hot melt processing andcoating, the adhesive can be crosslinked.

Typically, the crosslinker is a chemical crosslinker that generates freeradicals to affect the crosslinking reaction. One suitable class ofchemical crosslinkers is a photosensitive crosslinker which is activatedby high intensity ultraviolet (UV) light. Two common photosensitivecrosslinkers used for (meth)acrylate-based copolymers are benzophenoneand copolymerizable aromatic ketone monomers as described in U.S. Pat.No. 4,737,559. Typically, such crosslinkers are used in amounts of about0.05 to 1.0 parts by weight of crosslinker per 100 parts by weight oftotal monomers present in the pre-adhesive mixture.

Additionally, a photocrosslinking agent can be blended with thepre-adhesive mixture. This type of photocrosslinker does not polymerizeinto the (meth)acrylate based copolymer, but remains in the package andis not activated by the hot melt processing. An example of such aphotocrosslinker, which can be blended with the (meth)acrylate-basedcopolymer and activated by UV light, is a triazine, for example,2,4-bis(trichloromethyl)-6-(4-methoxy-phenyl)-s-triazine. Thesecrosslinkers, whether incorporated into the (meth)acrylate-basedcopolymer or blended with the copolymer, are activated by UV lightgenerated from artificial sources such as medium pressure mercury lampsor a UV blacklight.

The pre-adhesive mixture may also comprise a chain transfer agent.Examples of useful chain transfer agents include, but are not limitedto, those selected from the group consisting of carbon tetrabromide,mercaptans, alcohols, and mixtures thereof.

The pre-adhesive mixture may also comprise an initiator to initiate freeradical polymerization. Typically, the initiator is a thermal initiator.Thermal initiators useful in the present disclosure include, but are notlimited to azo, peroxide, persulfate, and redox initiators. In someembodiments, it may be desirable not to include an initiator and effectinitiation through the use of, for example, gamma radiation. In theseembodiments, the packaged pre-adhesive mixture is exposed to gammaradiation as described, for example, in pending application U.S. Ser.No. 61/737,221, filed Dec. 14, 2012.

Suitable azo initiators include, but are not limited to,2,2′-azobis(2,4-dimethylvaleronitrile) (VAZO 52);2,2′-azobisoisobutyronitrile) (VAZO 64);2,2′-azobis-2-methylbutyronitrile (VAZO 67); and(1,1′-azobis(1-cyclohexanecarbonitrile) (VAZO 88), all of which areavailable from DuPont Chemicals, and 2,2′-azobis(methyl isobutyrate)(V-601) and 2,2′-azobis(2-amidinopropane)dihydrochloride (V-50)available from Wako Chemicals. Also suitable is2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), formerly availablefrom DuPont Chemicals as VAZO 33.

Suitable peroxide initiators include, but are not limited to, benzoylperoxide, acetyl peroxide, lauroyl peroxide, decanoyl peroxide, dicetylperoxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate (PERKADOX16S, available from AKZO Chemicals), di(2-ethylhexyl) peroxydicarbonate,t-butylperoxypivalate (LUPERSOL 11, available from Atochem),t-butylperoxy-2-ethylhexanoate (TRIGONOX 21-050, available from AkzoChemicals, Inc.), and dicumyl peroxide.

Suitable persulfate initiators include, but are not limited to,potassium persulfate, sodium persulfate, and ammonium persulfate.

Suitable redox (oxidation-reduction) initiators include, but are notlimited to, combinations of the above persulfate initiators withreducing agents such as sodium metabisulfite and sodium bisulfite;systems based on organic peroxides and tertiary amines (for example,benzoyl peroxide plus dimethylaniline); and systems based on organichydroperoxides and transition metals, for example, cumene hydroperoxideplus cobalt naphthenate.

Other initiators include, but are not limited to pinacols, such astetraphenyl 1,1,2,2-ethanediol.

The thermal initiator may be used in an amount from about 0.01 to about5.0 parts by weight per 100 parts of total monomer, more typically from0.025 to 2 parts by weight per 100 parts of total monomer.

The adhesive composition may also comprise a variety of additives thatare not copolymerizable materials such as those described above as longas the additives do not interfere with the desired optical and adhesiveproperties of the adhesive composition. Crosslinking additives havealready been described above. Examples of other suitable additivesinclude tackifiers, plasticizers, and other performance enhancementadditives. Additionally, for optical applications, tackifiers,plastizicers and other additives should have low color; i.e. a Gardnervalue of greater than 3, more typically greater than 1.

Examples of useful tackifiers include, but are not limited to, rosin,rosin derivatives, polyterpene resins, coumarone-indene resins, and thelike. Plasticizers which may be added to the adhesive may be selectedfrom a wide variety of commercially available materials.

Representative plasticizers include polyoxyethylene aryl ether, dialkyladipate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenylphosphate, di-(2-ethylhexyl) adipate, toluenesulfonamide, dipropyleneglycol dibenzoate, polyethylene glycol dibenzoate, polyoxypropylene arylether, dibutoxyethoxyethyl formal, and dibutoxyethoxyethyl adipate. Whenused, tackifiers are preferably added in an amount not to exceed about50 parts by weight per 100 parts by weight copolymer, and plasticizermay be added in an amount up to about 50 parts by weight per 100 partsby weight copolymer.

It is desirable that any added tackifier and/or plasticizer has arefractive index of at least 1.50, so that incorporation does not reducethe refractive index of the adhesive. Useful high refractive indexplasticizers include aromatic phosphate esters, phtalates, benzoicethers, aromatic sulfonamide, and some rosins. The phosphate esters andphtalates are preferred. Exemplery plasticizer include diethylene glycoldibenzoate (1.5424 n25/D), 4-(tert-butyl)phenyl diphenyl phosphate(1.555 n25/D), trimethylphenyl phosphate (1.5545 n25/D), triphenylphosphate (1.5575 n25/D), phenylmethyl benzoate (1.56 n25/D), diethyleneglycol dibenzoate (1.5424 n25/D), butyl benzyl phthalate (1.537 n25/D),methyl ester of rosin (1.531 n20/D), alkyl benzyl phthalate (1.526n25/D), butyl(phenylsulfonyl)amine (1.525 n20/D), benzyl phthalate(1.518 n25/D), trimethyl trimellitate (1.523 (n20/D), and 2-ethylhexyldiphenyl phosphate (1.51 (n20/D).

Other additives can be added in order to enhance the performance of theadhesive compositions. Examples of such performance enhancing additivesinclude leveling agents, ultraviolet light absorbers, hindered aminelight stabilizers (HALS), oxygen inhibitors, wetting agents, rheologymodifiers, defoamers, biocides, dyes, pigments, and the like. All ofthese additives and the use thereof are well known in the art. It isunderstood that any of these compounds can be used so long as they donot deleteriously affect the adhesive and optical properties.

Among the particularly useful additives are UV absorbers and hinderedamine light stabilizers (HALS). UV absorbers and hindered amine lightstabilizers act to diminish the harmful effects of UV radiation on theadhesive composition and thereby enhance the weatherability, orresistance to cracking, yellowing and delamination of coatings preparedfrom the adhesive compositions. A suitable HALS isbis(1,2,2,6,6-pentamethyl-4-piperidinyl)[3,5-bis(1,1-dimethylethyl-4-hydroxyphenyl)methyl]butylpropanedioate,available as TINUVIN 144, from CIBA-GEIGY Corporation, Hawthorne, N.Y.

The following UV absorbers and combinations thereof in concentrations ofless than 5 parts by weight based on the total monomer composition, mayproduce desirable results, with concentrations in the range of 1-5 partsby weight based on the total monomer composition being particularlysuitable:bis(1,2,2,6,6-pentamethyl-4-piperidinyl)(3,5-bis(1,1-dimethylethyl1-4-hydroxyphenyl)methyl)butylpropanedioate,2-ethylhexyl-2-cyano-3,3′-diphenylacrylate,2-hydroxyl-4-n-octoxybenzophenone,2-(2′-hydroxy-5′-methylphenyl)benzotriazole, poly(oxy-1,2-ethanediyl),alpha-(3-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxylphenyl)-1-oxopropyl)-omega-hydroxy,and UVINUL D-50 and UVINUL MS-40, sold by BASF Wyandotte Inc.,Parsippany, N.J.

Additionally, the adhesive composition may also contain particles, aslong as the particles do not interfere with the desired opticalproperties of the adhesive composition. Particularly suitable areparticles that do not scatter visible light but absorb light of onewavelength and re-emit the light at a different wavelength. Examples ofsuch particles include the phosphor particles described in U.S. Pat. No.7,294,861 (Schardt et al.).

The packaged adhesive composition also comprises a packaging material.The packaging material completely surrounds the polymerized pre-adhesivemixture and any optional additives. The packaging material is athermoplastic material that generally melts at or below the processingtemperature of the polymerized pre-adhesive mixture (in other words, thetemperature at which the polymerized pre-adhesive mixture flows). Thepackaging material generally has a melting point of 200° C. or less, or170° C. or less. In some embodiments the melting point ranges from 90°C. to 150° C. The packaging material may be a flexible thermoplasticpolymeric film. The flexible thermoplastic polymeric films are preparedfrom thermoplastic materials. Suitable thermoplastic materials includepolyethylene, and ethylene copolymers such as ethylene/polyolefincopolymers and ethylene/vinyl copolymers such as ethylene vinyl acetate(EVA), ethylene methyl acrylate (EMA), ethylene acrylic acid (EAA), EAAionomers, and polypropylene, and other thermoplastic materials such asacrylics, polyphenylene ether, polyphenylene sulfide,acrylonitrile-butadiene-styrene copolymer (ABS), polyurethanes, andothers know to those skilled in the art. Blends of thermoplasticmaterials may also be used. Particularly suitable thermoplasticmaterials are polyethylene and EVA.

The flexible thermoplastic films range in thickness from 0.01 mm to 0.25mm. The thicknesses typically range from 0.025 mm to 0.127 mm to obtainfilms that have good strength during processing while being thin enoughto heat seal quickly and minimize the amount of film material used.

The packaging materials may contain plasticizers, stabilizers, dyes,perfumes, fillers, slip agents, antiblock agents, flame retardants,anti-static agents, microwave susceptors, thermally conductiveparticles, electrically conductive particles, and/or other materials toincrease the flexibility, handleability, visibility, or other usefulproperty of the film, as long as they do not adversely affect thedesired properties of the adhesive composition.

The amount of packaging material depends upon the type of material andthe desired end properties. The amount of packaging material typicallyranges from 0.5 to 20 weight % based on the total weight of the adhesivecomposition and the packaging material. Typically, the packagingmaterial is between 2 and 15 weight %, and more typically between 3 and5 weight %.

Also disclosed herein are methods of preparing packaged adhesivecompositions. These methods are similar to those described in U.S. Pat.No. 6,294,249 (Hamer et al.). In this method, a polymerizablepre-adhesive composition is prepared. The polymerizable pre-adhesivemixture comprises an aromatic monomer having a relatively highrefractive index and may also include a mixture of free radicallypolymerizable comonomers, a polymerization initiator, and optionaladditives as described above. This mixture can be prepared and mixed inany suitable mixing apparatus.

In some embodiments, two lengths of thermoplastic film are heat sealedtogether across the bottom and on each of the lateral edges on a liquidform-fill-seal machine to form an open ended pouch. The pre-adhesivecomposition is pumped through a hose to fill the pouch, and the pouch isthen heat sealed across the top to completely surround the adhesivecomposition.

Generally, the form-fill-seal machine is equipped with an impulse sealerto form the top and bottom seal across the pouches. Such a sealer hasone or two sets of jaws that clamp the pouch shut before scaling. Asealing wire is then heated to effect the seal, and the seal is cooledbefore the jaws are released. The sealing temperature is generally abovethe softening point and below the melting point of the film used to formthe pouch.

During the sealing process, it is desirable to get most of the air outof the pouch before sealing. A small amount of air is tolerable so longas the amount of oxygen is not sufficient to substantially interferewith the polymerization process. For ease of handling, it is desirableto seal the pouches as soon as they are filled with the composition,although immediate sealing is not necessary in all cases. In some casesthe pre-adhesive composition can alter the packaging material, and it isdesirable to cross-seal the pouches within about one minute of filling,more typically within 30 seconds, and most typically within 15 seconds.If the pre-adhesive composition decreases the strength of the packagingmaterial, it is desirable to polymerize the composition as soon aspossible after the pre-adhesive composition is surrounded by thepackaging material.

Alternatively, a single length of film can be folded lengthwise andsealed on one edge, filled with the pre-adhesive composition, andsealed. In another embodiment, a single length of film can be pulledthrough a forming collar, sealed to form a tube, filled with thecomposition, and sealed. Another embodiment can be carried out oncommercial liquid form-fill-seal machines. A source of such machines isthe Packaging Machinery Division of Eagle Corp. It is contemplated thatthe seals can be effected in any of a number of different configurationsto form multiple pouches across and down the lengths of film. Forexample, in addition to the seals on the lateral edges, a seal can alsobe formed down the center of the lengths of film so that a cross sealwill form two filled pouches. The pouches can either be left attached toeach other by the cross-seals and/or vertical seals, or they can be cutinto individual pouches or strands of pouches. The pouches may eachcontain the same or different compositions.

Thermal polymerization can be effected by immersing the packagedcomposition in a heat exchange medium at temperatures between about 40°C. and 100° C. for a time sufficient to polymerize the composition. Theheat exchange medium may be a forced or impinged gas or a liquid such aswater, perfluorinated liquids, glycerine, or propylene glycol. The heatnecessary for thermal polymerization may also be provided by a metalplaten, heated metal rolls, or microwave energy.

The temperature at which the polymerization occurs depends upon theactivation temperature of the initiator. It is desirable to carry outthe polymerization in an appropriate liquid heat exchange medium at acontrolled temperature. A suitable liquid heat exchange medium is water,heated to the desired reaction temperature. Commercially available heattransfer fluids may also be used.

Upon completion of the polymerization, a packaged adhesive compositionis generated. This packaged adhesive composition can be usedimmediately, stored for later use, or shipped to a different locationfor hot melt processing. Because the viscoelastic adhesive compositionis contained within a package, handling and storage is greatlysimplified.

Also disclosed herein, are articles comprising a substrate and anadhesive disposed on at least a portion of the substrate. The adhesivecomprises a (meth)acrylate-based copolymer having a refractive index ofat 1.48, and particles of a thermoplastic polymer, at least some of theparticles having an average particle size that is larger than thewavelength of visible light. The adhesive may be optically transparentor optically clear. The adhesives are described in detail above.

A wide variety of substrates are suitable for use in the articles ofthis disclosure. Because of the desirable optical properties of theadhesive, frequently the substrate is an optical substrate. As usedherein, the term “optical substrate” refers to a substrate that can beused to produce an optical effect. The substrate can be rigid,semi-rigid or flexible. The substrate can be any suitable thickness. Theoptical substrates often are at least partially transmissive,reflective, antireflective, polarizing, optically clear, or diffusivewith respect to some wavelengths of the electromagnetic spectrum (e.g.,wavelengths in the visible, ultraviolet, or infrared regions of theelectromagnetic spectrum). Exemplary optical substrates include, but arenot limited to, plates, sheets, the surfaces of optical articles, andfilms.

Examples of optically clear rigid and semi-rigid substrates includeplates, sheets, the surfaces of articles, and the like. The rigid orsemi-rigid substrate may be optically clear, optically transparent ornon-transparent. Examples of non-transparent substrates include onesthat are reflective scattering elements.

Examples of plates include a wide array of optically clear materials.Examples of suitable plates include a variety of glasses or frompolymeric materials such as polycarbonate or polymethyl methacrylate.The plates may be in a variety of thickness and may be flat or curved.In some embodiments, the plate may also comprise additional layers ortreatments. Examples of additional layers include, for example,additional layers of film designed to provide tinting, shatterresistance and the like. Examples of additional treatments that may bepresent include, for example, coatings or various types such ashardcoats.

Sheets are similar to plates but generally are thinner and less rigidthan plates. Examples of sheets include, for example, optically clearsemi-rigid substrates of glass or other optically clear materials thatare 25-100 micrometers in thickness.

Examples of substrates that are the surface of an article include, butare not limited to, the outer surface of an electronic display such asliquid crystal display or a cathode ray tube, an electronic device suchas a touch screen, an appliance such as a microwave oven (e.g. thetime/button display), the outer surface of a window or glazing, theouter surface of an optical component such as a reflector, polarizer,diffraction grating, mirror, or lens, or the like. The substrate cancontain polymeric materials, glass materials, ceramic materials,metal-containing materials (e.g., metals or metal oxides), or acombination thereof. Representative examples of polymeric materialsinclude polycarbonates, polyesters (e.g., polyethylene terephthalatesand polyethylene naphthalates), polyurethanes, poly(meth)acrylates(e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins suchas polyethylenes and polypropylenes, polyvinyl chlorides, polyimides,cellulose triacetates, acrylonitrile-butadiene-styrene copolymers, andthe like. The substrate may be a reflective scattering element.Reflective scattering elements are ones that exhibit diffuse orsemi-specular reflection. Diffuse and semi-specular reflections involvethe reflection of light from a surface such that an incident ray isreflected at many angles rather than at just one angle as in specularreflection. A wide array of materials can be used to prepare reflectivescattering elements, such as plaster, paper, fibrous materials such ascloth and non-woven fiber mats, inorganic filled reflective polymers,ceramic materials, crystalline surfaces, and voided polymeric materials.Examples of reflective scattering elements include graphics such assigns, markings or pictures; rough reflective surfaces of metals such asbrushed aluminum and chrome; coated surfaces such as painted, printed,or ink-coated surfaces.

Examples of flexible optical substrates include a wide array of opticalfilms. As used herein, the term “optical film” refers to a film that canbe used to produce an optical effect. The optical films are typicallypolymer-containing films that can be a single layer or multiple layers.The optical films can be of any suitable thickness. The optical filmsoften are at least partially transmissive, reflective, antireflective,polarizing, optically clear, or diffusive with respect to somewavelengths of the electromagnetic spectrum (e.g., wavelengths in thevisible ultraviolet, or infrared regions of the electromagneticspectrum). Exemplary optical films include, but are not limited to,visible mirror films, color mirror films, solar reflective films,diffusive films, infrared reflective films, ultraviolet reflectivefilms, reflective polarizer films such as brightness enhancement filmsand dual brightness enhancement films, absorptive polarizer films,optically clear films, tinted films, dyed films, privacy films such aslight-collimating films, and antireflective films, antiglare films, soilresistant films, and antifingerprint films.

In some embodiments the optical film has a coating. In general, coatingsare used to enhance the function of the film or provide additionalfunctionality to the film. Examples of coatings include, for example,hardcoats, anti-fog coatings, anti-scratch coatings, privacy coatings,anti-fingerprint coatings, antimicrobial coatings or a combinationthereof. Coatings such as hardcoats, anti-fog coatings, and anti-scratchcoatings that provide enhanced durability, are desirable in applicationssuch as, for example, touch screen sensors, display screens, graphicsapplications and the like. Examples of privacy coatings include, forexample, blurry or hazy coatings to give obscured viewing or louveredfilms to limit the viewing angle. Examples of anti-fingerprint coatingsinclude those described in pending U.S. Patent Application Ser. No.61/486,000 filed May 13, 2011 titled: “COATING COMPOSITIONS COMPRISINGNON-IONIC SURFACTANT EXHIBITING REDUCED FINGERPRINT VISIBILITY” whichdescribes coatings prepared from a curable resin and a non-ionicsurfactant. Examples of anti-microbial coatings include those describedin U.S. Pat. No. 8,124,169 (Ylitalo et al.) which describe anantimicrobial coating system that includes a film-forming compositionand an effective amount of an antimicrobial agent dispersed within thefilm-forming composition.

Some optical films have multiple layers such as multiple layers ofpolymer-containing materials (e.g., polymers with or without dyes) ormultiple layers of metal-containing material and polymeric materials.Some optical films have alternating layers of polymeric material withdifferent refractive indices. Other optical films have alternatingpolymeric layers and metal-containing layers. Exemplary optical filmsare described in the following patents: U.S. Pat. No. 6,049,419(Wheatley et al.); U.S. Pat. No. 5,223,465 (Wheatley et al.); U.S. Pat.No. 5,882,774 (Jonza et al.); U.S. Pat. No. 6,049,419 (Wheatley et al.);U.S. Pat. No. RE 34,605 (Schrenk et al.); U.S. Pat. No. 5,579,162(Bjornard et al.), and U.S. Pat. No. 5,360,659 (Arends et al.).

In some embodiments, the optical film comprises a multilayer paintprotection film suitable for use with automobiles and other relateduses. Examples of suitable films include those described, for example inUS Patent Publication No. 2008/0199704 (Ho et al.). These multilayerfilms contain polyurethanes that are lightly crosslinked but are notthermosets. These multilayer films are typically transparent, andpossibly even translucent, for paint protection applications, or evenopaque for other surface protection or enhancement applications. Forsome applications, it may be desirable for the multilayer film to becolored. When used as a paint protection film, it is often desirable forthe multilayer film to be sized and shaped to conform to the surface tobe protected, before the film is applied. Pre-sized and shaped pieces ofthe multilayer film can be commercially desirable for protecting thepainted surface of various body parts of a vehicle such as, for example,an automobile, aircraft, watercraft, etc., especially those portions ofthe vehicle body (e.g., the leading edge of the front hood and otherleading surfaces, rocker panels, etc.) that are exposed to such hazardsas flying debris (e.g., sand, rocks, etc.), insects, or the like.

Particularly suitable articles are those where the substrate comprises afilm, a tape backing, a graphic article, a light guide, a plasticarticle, a wound dressing, a protection film or tape, a light extractionlayer, a keypad or membrane switch, a heat shrinkable layer orsubstrate, a display, a touch sensor, or a moldable film.

Also disclosed herein are methods for preparing adhesive articlescomprising providing a hot melt processable packaged adhesivecomposition, hot melt processing the packaged adhesive composition, anddisposing the hot melt processed packaged adhesive composition on asubstrate. The adhesive composition comprises a (meth)acrylate-basedcopolymer having a refractive index of at 1.48, and particles of athermoplastic polymer, at least some of the particles having an averageparticle size that is larger than the wavelength of visible light. Theadhesive may be optically transparent or optically clear. The adhesivesare described in detail above.

Methods of preparing hot melt processable packaged adhesive compositionsare described in detail above. These packaged adhesive compositions arehot melt processed through the use of a hot melt mixing apparatus.

A variety of hot melt mixing techniques using a variety of hot meltmixing equipment are suitable for processing the packaged adhesivecompositions. Both batch and continuous mixing equipment may be used.Examples of batch methods include those using a BRABENDER (e. g. aBRABENDER PREP CENTER, commercially available from C.W. BrabenderInstruments, Inc.; South Hackensack, N.J.) or BANBURY internal mixingand roll milling equipment (e.g. equipment available from Farrel Co.;Ansonia, Conn.). Examples of continuous methods include single screwextruding, twin screw extruding, disk extruding, reciprocating singlescrew extruding, and pin barrel single screw extruding. Continuousmethods can utilize distributive elements, pin mixing elements, staticmixing elements, and dispersive elements such as MADDOCK mixing elementsand SAXTON mixing elements. A single hot melt mixing apparatus may beused, or a combination of hot melt mixing equipment may be used toprocess the packaged adhesive compositions of this disclosure.

The output of the hot melt mixing is coated onto a substrate to form anadhesive layer. If a batch apparatus is used, the resulting hot meltblend can be removed from the apparatus and placed in a hot melt coateror extruder and coated onto a substrate. If an extruder is used toprepare a hot melt blend, the blend can be directly extruded onto asubstrate to form an adhesive layer in a continuous forming method. Inthe continuous forming method, the adhesive can be drawn out of a filmdie and subsequently contacted to a moving plastic web or other suitablesubstrate. If the adhesive is to be part of a tape, the substrate may bea tape backing. In some methods, the tape backing material is coextrudedwith the adhesive from a film die and the multilayer construction isthen cooled to form the tape in a single coating step. If the adhesiveis to be a transfer tape, the adhesive layer may be a free standing filmand the substrate may be a release liner or other releasing substrate.After forming, the adhesive layer or film can be solidified by quenchingusing both direct methods (e.g. chill rolls or water batch) and indirectmethods (e.g. air or gas impingement).

If it is desired to crosslink the pressure sensitive adhesive layer, theadhesive layer can be subjected to a crosslinking process. If aphotosensitive crosslinker is present, such as those described above,the adhesive layer can be exposed to high intensity UV lamps to effectcrosslinking. If no crosslinker is present, crosslinking may be achievedby exposing the adhesive layer to high-energy electromagnetic radiationsuch as gamma or e-beam radiation.

The disclosure includes the following embodiments:

Among the embodiments are adhesive compositions. The first embodimentincludes an adhesive composition comprising: a (meth)acrylate-basedcopolymer having a refractive index of at least 1.48; particles of athermoplastic polymer, at least some of the particles having an averageparticle size that is larger than the wavelength of visible light,wherein the adhesive composition is optically transparent.

Embodiment 2 is the adhesive composition of embodiment 1, wherein theadhesive composition is optically clear, having a visible lighttransmission of greater than 90%, and a haze of less than 5%.

Embodiment 3 is the adhesive composition of embodiment 1 or 2, whereinthe particles of thermoplastic polymer comprise particles ofpolyethylene, ethylene vinyl acetate, ethylene methyl acrylate, ethyleneacrylic acid, ethylene acrylic acid ionomers, polypropylene, acrylicpolymers, polyphenylene ether, polyphenylene sulfide,acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixturesand blends thereof.

Embodiment 4 is the adhesive composition of any of embodiments 1-3,wherein the particles of thermoplastic polymer comprise particle ofpolyethylene, ethylene vinyl acetate, or mixtures or blends thereof.

Embodiment 5 is the adhesive composition of any of embodiments 1-4,wherein the (meth)acrylate-based copolymer comprises a copolymer of anaromatic monomer in an amount of at least 5 parts per 100 parts of totalmonomer, the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is unsubstituted or substitutedwith a substituent selected from the group consisting of Br_(y) and(R³)_(z) wherein y represents the number of bromine substituentsattached to the aromatic group and is an integer from 0 to 3; R³ is astraight or branched alkyl of 2 to 12 carbons; and z represents thenumber of R³ substituents attached to the aromatic ring and is aninteger from 0 to 1, provided that both y and z are not zero; X isoxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl; n is 0 to 3; R¹is an unsubstituted straight or branched alkyl linking group of 2 to 12carbons; and R² is either H or CH₃.

Embodiment 6 is the adhesive composition of any of embodiments 1-5,further comprising at least one acrylic monomer selected from the groupconsisting of monomeric acrylic or methacrylic acid ester of anon-tertiary alkyl alcohol of about 1 to about 12 carbons.

Embodiment 7 is the adhesive composition of any of embodiments 1-6,further comprising at least one polar monomer copolymerizable with thearomatic monomer(s).

Embodiment 8 is the adhesive composition of embodiment 6, wherein theacrylic monomer is selected from the group consisting of 1-butanol,1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol,1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol,1-dodecanol, and mixtures thereof.

Embodiment 9 is the adhesive composition of embodiment 7, wherein thepolar monomer(s) are selected from the group consisting of ethylenicallyunsaturated carboxylic acids, ethylenically unsaturated sulfonic acids,ethylenically unsaturated phosphoric acids, acrylamides, N,N-dialkylsubstituted acrylamides, N-vinyl lactams, and N,N-dialkylaminoalkylacrylates, ethylenically unsaturated nitriles, and mixtures thereof.

Embodiment 10 is the adhesive composition of embodiment 5, wherein thearomatic monomer(s) are selected from the group consisting of6-(4,6-dibromo-2-isopropyl phenoxy)-1-hexyl acrylate,6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexyl acrylate,2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl phenylacrylate, 2-(1-naphthyloxy)-1-ethyl acrylate, 2-(2-naphthyloxy)-1-ethylacrylate, 6-(1-naphthyloxy)-1-hexyl acrylate, 6-(2-naphthyloxy)-1-hexylacrylate, 8-(1-naphthyloxy)-1-octyl acrylate, 8-(2-naphthyloxy)-1-octylacrylate, and phenoxy ethyl acrylate.

Embodiment 11 is the adhesive composition of any of embodiments 1-10,wherein the adhesive composition is crosslinked.

Among the embodiments are packaged adhesive compositions. Embodiment 12is a packaged adhesive composition comprising: a polymerizedpre-adhesive mixture, wherein the polymerizable pre-adhesive compositioncomprises: an aromatic monomer in an amount of at least 5 parts per 100parts of total monomer, the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is unsubstituted or substitutedwith a substituent selected from the group consisting of Br_(y) and(R³)_(z) wherein y represents the number of bromine substituentsattached to the aromatic group and is an integer from 0 to 3; R³ is astraight or branched alkyl of 2 to 12 carbons; and z represents thenumber of R³ substituents attached to the aromatic ring and is aninteger from 0 to 1, provided that both y and z are not zero; X isoxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl; n is 0 to 3; R¹is an unsubstituted straight or branched alkyl linking group of 2 to 12carbons; and R² is either H or CH₃; and a packaging material.

Embodiment 13 is the packaged adhesive composition of embodiment 12,wherein the packaging material comprises polyethylene, ethylene vinylacetate, ethylene methyl acrylate, ethylene acrylic acid, ethyleneacrylic acid ionomers, polypropylene, acrylic polymers, polyphenyleneether, polyphenylene sulfide, acrylonitrile-butadiene-styrenecopolymers, polyurethanes, and mixtures and blends thereof.

Embodiment 14 is the packaged adhesive composition of embodiment 12 or13, wherein the packaging material comprises polyethylene, ethylenevinyl acetate, or mixtures or blends thereof.

Embodiment 15 is the packaged adhesive composition of any of embodiments12-14, wherein the polymerizable pre-adhesive mixture further comprisesat least one acrylic monomer selected from the group consisting ofmonomeric acrylic or methacrylic acid ester of a non-tertiary alkylalcohol of about 1 to about 12 carbons.

Embodiment 16 is the packaged adhesive composition of embodiment 15,wherein the acrylic monomer is selected from the group consisting of1-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol,1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol,3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol,1-dodecanol, and mixtures thereof.

Embodiment 17 is the packaged adhesive composition of any of embodiments12-16, wherein the polymerizable pre-adhesive mixture further comprisesat least one polar monomer copolymerizable with the aromatic monomer(s).

Embodiment 18 is the packaged adhesive composition of embodiment 17,wherein the polar monomer(s) are selected from the group consisting ofethylenically unsaturated carboxylic acids, ethylenically unsaturatedsulfonic acids, ethylenically unsaturated phosphoric acids, acrylamides,N,N-dialkyl substituted acrylamides, N-vinyl lactams, andN,N-dialkylaminoalkyl acrylates, ethylenically unsaturated nitriles, andmixtures thereof.

Embodiment 19 is the packaged adhesive composition of embodiment 12,wherein the aromatic monomer(s) are selected from the group consistingof 6-(4,6-dibromo-2-isopropyl phenoxy)-1-hexyl acrylate,6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexyl acrylate,2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl phenylacrylate, 2-(1-naphthyloxy)-1-ethyl acrylate, 2-(2-naphthyloxy)-1-ethylacrylate, 6-(1-naphthyloxy)-1-hexyl acrylate, 6-(2-naphthyloxy)-1-hexylacrylate, 8-(1-naphthyloxy)-1-octyl acrylate, 8-(2-naphthyloxy)-1-octylacrylate, and phenoxy ethyl acrylate.

Among the embodiments are articles. Embodiment 20 is an articlecomprising: a substrate; and an adhesive disposed on at least a portionof the substrate, the adhesive comprising: a (meth)acrylate-basedcopolymer having a refractive index of at least 1.48; particles of athermoplastic polymer, at least some of the particles having an averageparticle size that is larger than the wavelength of visible light,wherein the adhesive composition is optically transparent.

Embodiment 21 is the article of embodiment 20, wherein the adhesivecomposition is optically clear, having a visible light transmission ofgreater than 90%, and a haze of less than 5%.

Embodiment 22 is the article of embodiment 20 or 21, wherein thesubstrate comprises a film, a tape backing, a graphic article, a lightguide, a plastic article, a wound dressing, a protection film or tape, alight extraction layer, a keypad or membrane switch, a heat shrinkablelayer or substrate, a display, a touch sensor, or a moldable film.

Embodiment 23 is the article of any of embodiments 20-22, wherein theparticles of thermoplastic polymer comprise particles of polyethylene,ethylene vinyl acetate, ethylene methyl acrylate, ethylene acrylic acid,ethylene acrylic acid ionomers, polypropylene, acrylic polymers,polyphenylene ether, polyphenylene sulfide,acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixturesand blends thereof.

Embodiment 24 is the article of any of embodiments 20-23, wherein theparticles of thermoplastic polymer comprise particle of polyethylene,ethylene vinyl acetate, or mixtures or blends thereof.

Embodiment 25 is the article of any of embodiments 20-24, wherein the(meth)acrylate-based copolymer comprises a copolymer an aromatic monomerin an amount of at least 5 parts per 100 parts of total monomer, thearomatic monomer having the formula:

wherein: Ar is an aromatic group which is unsubstituted or substitutedwith a substituent selected from the group consisting of Br_(y) and(R³)_(z) wherein y represents the number of bromine substituentsattached to the aromatic group and is an integer from 0 to 3; R³ is astraight or branched alkyl of 2 to 12 carbons; and z represents thenumber of R³ substituents attached to the aromatic ring and is aninteger from 0 to 1, provided that both y and z are not zero; X isoxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl; n is 0 to 3; R¹is an unsubstituted straight or branched alkyl linking group of 2 to 12carbons; and R² is either H or CH₃.

Embodiment 26 is the article of any of embodiments 20-25, wherein theadhesive is crosslinked.

Among the embodiments are methods of preparing an adhesive article.Embodiment 27 is a method of preparing an adhesive article comprising:providing a hot melt processable packaged adhesive compositioncomprising a hot melt processable (meth)acrylate-based copolymer havinga refractive index of at least 1.48, and a packaging material; hot meltprocessing the packaged adhesive composition; and disposing the hot meltprocessed packaged adhesive composition on a substrate, wherein theadhesive composition is optically transparent.

Embodiment 28 is the method of embodiment 27, wherein the adhesivecomposition is optically clear, having a visible light transmission ofgreater than 90%, and a haze of less than 5%.

Embodiment 29 is the method of embodiment 27 or 28, wherein providing ahot melt processable packaged adhesive composition comprises: combininga polymerizable pre-adhesive reactive mixture and a packaging materialto form a packaged pre-adhesive composition, the pre-adhesive mixturecomprising an aromatic monomer in an amount of at least 5 parts per 100parts of total monomer, the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is unsubstituted or substitutedwith a substituent selected from the group consisting of Br_(y) and(R³)_(z) wherein y represents the number of bromine substituentsattached to the aromatic group and is an integer from 0 to 3; R³ is astraight or branched alkyl of 2 to 12 carbons; and z represents thenumber of R³ substituents attached to the aromatic ring and is aninteger from 0 to 1, provided that both y and z are not zero; X isoxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl; n is 0 to 3; R¹is an unsubstituted straight or branched alkyl linking group of 2 to 12carbons; and R² is either H or CH₃; and polymerizing the pre-adhesivemixture.

Embodiment 30 is the method of any of embodiments 27-29, wherein thepackaging material comprises polyethylene, ethylene vinyl acetate,ethylene methyl acrylate, ethylene acrylic acid, ethylene acrylic acidionomers, polypropylene, acrylic polymers, polyphenylene ether,polyphenylene sulfide, acrylonitrile-butadiene-styrene copolymers,polyurethanes, and mixtures and blends thereof.

Embodiment 31 is the method of any of embodiments 27-30, wherein thepackaging material comprises polyethylene, ethylene vinyl acetate, ormixtures or blends thereof.

Embodiment 32 is the method of embodiment 29, wherein the polymerizablepre-adhesive mixture further comprises at least one acrylic monomerselected from the group consisting of monomeric acrylic or methacrylicacid ester of a non-tertiary alkyl alcohol of about 1 to about 12carbons.

Embodiment 33 is the method of embodiment 32, wherein the acrylicmonomer is selected from the group consisting of 1-butanol, 1-pentanol,2-pentanol, 3-pentanol, 2-methyl-1-butanol, 1-methyl-1-butanol,1-methyl-1-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol,2-ethyl-1-butanol, 2-ethyl-1-hexanol, 3,5,5-trimethyl-1-hexanol,3-heptanol, 2-octanol, 1-decanol, 1-dodecanol, and mixtures thereof.

Embodiment 34 is the method of embodiment 29, wherein the polymerizablepre-adhesive mixture further comprises at least one polar monomercopolymerizable with the aromatic monomer(s).

Embodiment 35 is the method of embodiment 34, wherein the polarmonomer(s) are selected from the group consisting of ethylenicallyunsaturated carboxylic acids, ethylenically unsaturated sulfonic acids,ethylenically unsaturated phosphoric acids, acrylamides, N,N-dialkylsubstituted acrylamides, N-vinyl lactams, and N,N-dialkylaminoalkylacrylates, ethylenically unsaturated nitriles, and mixtures thereof.

Embodiment 36 is the method of embodiment 29, wherein the aromaticmonomer(s) are selected from the group consisting of6-(4,6-dibromo-2-isopropyl phenoxy)-1-hexyl acrylate,6-(4,6-dibromo-2-sec-butyl phenoxy)-1-hexyl acrylate,2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl phenylacrylate, 2-(1-naphthyloxy)-1-ethyl acrylate, 2-(2-naphthyloxy)-1-ethylacrylate, 6-(1-naphthyloxy)-1-hexyl acrylate, 6-(2-naphthyloxy)-1-hexylacrylate, 8-(1-naphthyloxy)-1-octyl acrylate, 8-(2-naphthyloxy)-1-octylacrylate, and phenoxy ethyl acrylate.

Embodiment 37 is the method of any of embodiments 27-36, wherein thesubstrate comprises a film, a tape backing, a graphic article, a lightguide, a plastic article, a wound dressing, a protection film or tape, alight extraction layer, a keypad or membrane switch, a heat shrinkablelayer or substrate, a display, a touch sensor, or a moldable film.

Embodiment 38 is the method of any of embodiments 27-37, furthercomprising crosslinking the adhesive disposed on the substrate.

Embodiment 39 is the method of embodiment 38, wherein crosslinkingcomprises photochemical initiation of a crosslinker, or exposure togamma radiation or an electron beam.

Embodiment 40 is the method of embodiment 29, wherein polymerization ofthe pre-adhesive mixture comprises thermal initiation of an initiator,or exposure to gamma radiation.

Embodiment 41 is the method of any of embodiments 27-40, wherein hotmelt processing comprises extrusion in an extruder and the resultingdisposed adhesive comprises: a (meth)acrylate copolymer having arefractive index of at least 1.48; particles of a thermoplastic polymer,at least some of the particles having an average particle size that islarger than the wavelength of visible light.

Embodiment 42 is the method of embodiment 41, further comprising theaddition of at least one additive to the extruder.

Embodiment 43 is the method of any of embodiments 27-42, wherein hotmelt processing comprises extrusion in an extruder and disposing the hotmelt processed packaged adhesive composition on a substrate comprisessimultaneous extrusion of the hot melt processed packaged adhesivecomposition and the substrate.

Examples

Optical adhesive formulations were prepared, coated, and tested to showadhesive properties while maintaining acceptable transmission, clarityand haze values. Pouch domain size within the adhesive was alsoevaluated. These examples are merely for illustrative purposes only andare not meant to be limiting on the scope of the appended claims. Allparts, percentages, ratios, etc. in the examples and the rest of thespecification are by weight, unless noted otherwise.

Materials:

Abbre- viation Description M1 Monomer, Isooctyl acrylate, commerciallyavailable from CPS Chemical Co., Old Bridge, NJ. M2 Monomer, Acrylicacid, commercially available from BASF Corporation, Pasippany, NJ M3Monomer, 2-biphenyloxyethyl acrylate commercially available fromToagosei Co., Ltd., Tokyo, Japan CTA Chain Transfer Agent,Isooctylthioglycolate commercially available from Ciba/BASF, Hawthorne,NY PI1 Photoinitiator, commercially available from Ciba/BASF, Hawthorne,NY as “IRGACURE 651” PI2 Photoinitiator, commercially available fromCiba/BASF, Hawthorne, NY as “IRGACURE 1076”. M4 Monomer,Acryloxybenzophenone, commercially available from Ciba/BASF, Hawthorne,NY P1 Polymeric ionic crosslinker as described in U.S. Pat. No.6,800,680 (Stark) “Basic Copolymer J” except that 2 ethylhexyl acrylate(#290815 available from Sigma Aldrich, St. Louis, MO) was used insteadof IOA. P2 Octene plastomer commercially available from ExxonMobilChemical, Baytown, TX as “EXACT 8203” M5 Monomer, N,N-Dimethylacrylamidecommercially available from Sigma Aldrich, St. Louis, MO M6 Monomer,2-ethylhexyl acrylate commercially available from Sigma Aldrich, St.Louis, MO

FORMULATION TABLE Formu- lation Components (parts by weight) F1 M1/M2(94/6) + 0.15 PI 1 + 0.20 PI 2 + 0.15 M4 F2 M6/M2 (90/10) + 0.03 CTA +0.15 PI 1 F3 M1/M2/M3 (89/6/5) + 0.15 PI 1 + 0.20 PI 2 + 0.15 M4 F4M1/M2/M3 (84/6/10) + 0.15 PI 1 + 0.20 PI 2 + 0.15 M4 F5 M1/M2/M3(74/6/20) + 0.15 PI 1 + 0.20 PI 2 + 0.15 M4 F6 M1/M2/M3 (72/3/25) + 0.08CTA F7 M1/M2/M3 (70/5/25) + 0.03 CTA + 0.15 PI 1 F8 M1/M2/M3 (65/5/30) +0.03 CTA + 0.15 PI 1 F9 M1/M2/M3 (64/6/30) + 0.15 PI 1 + 0.20 PI 2 +0.15 M4 F10 M1/M2/M3 (80/5/15) + 0.02 CTA + 0.15 PI 1 + 0.20 PI 2 + 0.15M4 F11 M1/M2/M3 (80/5/15) + 0.02 CTA + 0.15 PI 1 + 0.20 PI 2 + 0.15 M4 +11.15 P2 F12 M1/M2/M3 (80/5/15) + 0.03 CTA + 0.15 PI 1 + 0.20 PI 2 +2.00 PI F13 M1/M2/M3 (77/6/15) + 0.04 CTA + 0.15 PI 1 + 0.20 PI 2 + 0.15M4 + 2.00 M5Test MethodsPeel Adhesion (ASTM D3330 PSTC 101)

Peel adhesion is the force required to remove a coated flexible sheetmaterial from a test panel measured at a specific angle and rate ofremoval. In the examples, the methods of sample preparation and testingare modifications of ASTM method D 3330 (1992) and Pressure SensitiveTape Council method PSTC-101 (1989). Adhesive extruded onto urethanefilm was equilibrated under ambient conditions for 1 week. One day priorto testing samples, samples were exposed to a constant temperature andhumidity, 23° C. and 50% relative humidity. The samples were cut into 10millimeter wide strips. Isopropyl alcohol was used to clean RK8014 paintpanels (available from ACT, Hillsdale, Mich.) The release liner wasremoved and the adhesive strips were applied to the RK8014 panels usinga squeegee. Peel adhesion was measured about 20 minutes afterapplication as a 180 degree peel back at a crosshead speed of 30 cm/minusing Model 1122 tensile tester (available from Modular Test Systems,Shakopee, Minn.). The peel adhesion was measured in ounces per inch andconverted to Newtons per meter (N/m).

Total Transmission and Haze (ASTM D1003)

Luminous transmission, clarity and haze were measured according to ASTMD1003-00 using a Gardner Haze-Guard Plus model 4725 (available fromBYK-Gardner Columbia, Md.). The adhesive was sandwiched between 2 films(as noted in the Example section) and % transmission, % haze, and %clarity values were recorded.

EXAMPLES Adhesive Preparation

The adhesive compositions were prepared using the procedures describedin U.S. Pat. No. 6,294,249 (Hamer et al.) incorporated herein byreference. Two sheets of ethylene vinyl acetate film, (available fromBerry Plastics Corporation, Evansville, Ind.) were heat sealed on thelateral edges and the bottom to form a rectangular pouch measuring 3.175cm wide on a liquid form, fill, and seal machine, Schlosspack Form FillSeal Model # VM220HS. The pouch was then filled with the adhesivecomposition in the solids weight percentages specified in theFormulation Table. The filled package was then heat sealed at the top inthe cross direction through the monomer to form individual adhesivepouches measuring 3.175 cm by 3.175 cm by about 0.356 cm thickcontaining approximately 25 grams of composition.

The adhesive pouches were placed in a water bath that was maintainedbetween about 15° C. and 17° C. and exposed to ultraviolet radiation atan intensity of about 4.5 mW/cm² for 8.33 minutes. The radiation wassupplied by lamps having about 90% of the emission between 300 and 400nm and peak emission at 351 nm.

Examples 1-8 and Comparative Examples C1-C2

Using the formulations and conditions in Table 1, adhesive pouches werefed into a twin screw extruder (Werner Pfleiderer) with barreltemperatures set to 177° C. Adhesives were extruded from a drop die to athickness of 51 micrometers onto a polyurethane film (prepared asdescribed in example 1 of PCT Publication No. WO 2006/118883 (Ho)). Asnoted in Table 1 some of the coated adhesives samples were then exposedto ultraviolet radiation. The coated adhesive samples were wound into aroll while inserting a paper web that was treated on both sides with asilicone release coating. The coated adhesives were tested for luminanceand peel adhesion using the test methods described above. Results arerecorded in Table 1. 165 micrometer PET film with 1.5% haze, 89%transmission, and 99.6% clarity was laminated to the adhesive side ofthe samples before luminance testing.

TABLE 1 Peel Adhesion, Haze, Transmission and Clarity data for Examples1-8 and Comparative Examples C1-C2 UVC % % Trans- % Peel Example#Formulation# mJ/cm² Haze mission Clarity (N/m) E1 F3 0 8.9 89.4 95.31104 E2 F3 20 9.7 89.9 95.5 820 E3 F4 0 8.7 89.8 96.5 1063 E4 F5 0 3.989.8 98.1 1222 E5 F9 0 2.6 89.9 98.7 1000 E6 F11 0 4.2 90.0 99.6 1015 E7F12 0 6.2 89.7 97.5 720 E8 F13 0 4.3 89.8 98.0 1244 Comparative F1 016.4 88.9 93.8 1087 Example C1 Comparative F1 20 14.9 88.9 93.8 887Example C2

Example 9

Using the formulation and conditions in Table 2, adhesive pouches werefed into a twin screw extruder (Werner Pfleiderer) with barreltemperatures set to 177° C. Polyurethane pellets (ESTANE ALR CL87AVavailable from Lubrizol Corporation, Wickliffe, Ohio) were fed into asingle screw extruder (Haake) with barrel temperatures set to 177° C.The 2 melt streams were fed into a multi-layer die and extruded onto apaper web that was treated on both sides with a silicone releasecoating. Intralayer bubbles were observed in the extruded sample. Thepolyurethane was 152 micrometers thick and the adhesive sample was 51micrometers thick. The coated adhesive sample was then exposed toultraviolet radiation. The adhesive was tested for luminance and peeladhesion using the test methods described above. Results are recorded inTable 2. 165 micrometer PET film with 1.5% haze, 89% transmission, and99.6% clarity was laminated to the adhesive side of the samples beforeluminance testing.

TABLE 2 Peel Adhesion, Haze, Transmission and Clarity data for Example 9UVC % % Trans- % Peel Example# Formulation# mJ/cm² Haze mission Clarity(N/m) E9 F10 30 10.1 89.8 94.9 395

Example 10-12 and Comparative Example 3

Using the formulation and conditions in Table 3, adhesive pouches wereprocessed through a ram extruder into a static mixer both set to 177° C.The adhesives were extruded from a drop die set at 188° C. The adhesivewas extruded onto a paper web that was treated on both sides with asilicone release coating. See the formulations and conditions in Table3. The adhesive samples were then exposed to ultraviolet or gammaradiation. The ultraviolet radiation was supplied by medium pressuremercury vapor lamps having an output of about 80 watts per cm andspectral output over a range of 180 to 430 nm to provide a total energyof ˜250 mJ/cm². The adhesives were tested for luminance using the testmethod described above. Results are recorded in Table 3. 51 micrometerprimed PET film (HOSTAPHAN available from Mitsubishi Polyester FilmInc., Greer, S.C.) with 4.9% haze, 90.7% transmission, and 95.9% claritywas laminated to both sides of the adhesive samples before luminancetesting.

TABLE 3 Haze, Transmission and Clarity data for Examples 10-12 andComparative Example C3 Polymerization Thickness Exam- Formu- Method &(micro- % % Trans- % ple# lation# Energy meters) Haze mission ClarityCom- F2 UV 250 109.5 38.1 86.8 88.1 parative (mJ/cm²) Example C3 E10 F6Gamma 5.8 89.7 4.9 87.5 97.9 (kGy) E11 F7 UV 250 97.3 6.4 87.6 99.0(mJ/cm²) E12 F8 UV 250 233.2 4.7 86.5 96.5 (mJ/cm²)Micrographs to Determine Phase Size

An approximate 51 mm by 51 mm sample of adhesive only, Formulation 10,Example 9, was cut and placed onto a glass slide under a Zeissmicroscope available from System Eickhost, Hamburg, Germany. Micrographswere taken at a magnification of 78.75 times. Using IMAGEJ 1.44Ksoftware, available by National Institute of Health, the height andwidth of the extruded pouch material were measured and averaged todetermine the materials domain size within the adhesive.

Results from measuring 2015 extruded pouch domains were averaged. Theaverage height was 0.9194 micrometers and the average width was 0.3138micrometers.

What is claimed is:
 1. An adhesive composition comprising: a(meth)acrylate-based copolymer having a refractive index of at least1.48; particles of a thermoplastic polymer, at least some of theparticles having an average particle size that is larger than thewavelength of visible light, wherein the refractive index of the(meth)acrylate-based copolymer and the thermoplastic polymer particlesare matched, and wherein the adhesive composition is opticallytransparent.
 2. The adhesive composition of claim 1, where the adhesivecomposition is optically clear, having a visible light transmission ofgreater than 90%, and a haze of less than 5%.
 3. The adhesivecomposition of claim 1, wherein the particles of thermoplastic polymercomprise particles of polyethylene, ethylene vinyl acetate, ethylenemethyl acrylate, ethylene acrylic acid, ethylene acrylic acid ionomers,polypropylene, acrylic polymers, polyphenylene ether, polyphenylenesulfide, acrylonitrile-butadiene-styrene copolymers, polyurethanes, andmixtures and blends thereof.
 4. The adhesive composition of claim 1,wherein the (meth)acrylate-based copolymer comprises a copolymer of anaromatic monomer in an amount of at least 5 parts per 100 parts of totalmonomer, the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is an unsubstituted phenyl group,a substituted or unsubstituted fused or linked aromatic group, or asubstituted phenyl group with a substituent selected from the groupconsisting of Br_(y) and (R³)_(z) wherein y represents the number ofbromine substituents attached to the aromatic group and is an integerfrom 0 to 3; R³ is a straight or branched alkyl of 2 to 12 carbons; andz represents the number of R³ substituents attached to the aromatic ringand is an integer from 0 to 1, provided that both y and z are not zero;X is oxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄ alkyl; n is 0 to3; R¹ is an unsubstituted straight or branched alkyl linking group of 2to 12 carbons; and R² is either H or CH₃.
 5. The adhesive composition ofclaim 4, further comprising at least one acrylic monomer selected fromthe group consisting of monomeric acrylic or methacrylic acid ester of anon-tertiary alkyl alcohol of 1 to 12 carbons.
 6. The adhesivecomposition of claim 4, wherein the aromatic monomer(s) are selectedfrom the group consisting of 6-(4,6-dibromo-2-isopropyl phenoxy) hexylacrylate, 6-(4,6-dibromo-2-sec-butyl phenoxy) hexyl acrylate,2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl phenylacrylate, 2-(1-naphthyloxy) ethyl acrylate, 2-(2-naphthyloxy) ethylacrylate, 6-(1-naphthyloxy) hexyl acrylate, 6-(2-naphthyloxy) hexylacrylate, 8-(1-naphthyloxy) octyl acrylate, 8-(2-naphthyloxy) octylacrylate, and phenoxy ethyl acrylate.
 7. The adhesive composition ofclaim 1, wherein the adhesive composition is crosslinked.
 8. A packagedadhesive composition comprising: a polymerized polymerizablepre-adhesive mixture, wherein the polymerizable pre-adhesive compositioncomprises: an aromatic monomer in an amount of at least 5 parts per 100parts of total monomer, the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is an unsubstituted phenyl group,a substituted or unsubstituted fused or linked aromatic group, or asubstituted phenyl group substituted with a substituent selected fromthe group consisting of Br_(y) and (R³)_(z) wherein y represents thenumber of bromine substituents attached to the aromatic group and is aninteger from 0 to 3; R³ is a straight or branched alkyl of 2 to 12carbons; and z represents the number of R³ substituents attached to thearomatic ring and is an integer from 0 to 1, provided that both y and zare not zero; X is oxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄alkyl; n is 0 to 3; R¹ is an unsubstituted straight or branched alkyllinking group of 2 to 12 carbons; and R² is either H or CH₃; wherein thepolymerized polymerizable composition has a refractive index of at least1.48; and a packaging material, wherein the refractive index of thepolymerized polymerizable composition and the refractive index of thepackaging material are matched.
 9. The packaged adhesive composition ofclaim 8, wherein the polymerizable pre-adhesive mixture furthercomprises at least one acrylic monomer selected from the groupconsisting of monomeric acrylic or methacrylic acid ester of anon-tertiary alkyl alcohol of 1 to 12 carbons.
 10. The packaged adhesivecomposition of claim 8, wherein the aromatic monomer(s) are selectedfrom the group consisting of 6-(4,6-dibromo-2-isopropyl phenoxy) hexylacrylate, 6-(4,6-dibromo-2-sec-butyl phenoxy) hexyl acrylate,2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecyl phenylacrylate, 2-(1-naphthyloxy) ethyl acrylate, 2-(2-naphthyloxy) ethylacrylate, 6-(1-naphthyloxy) hexyl acrylate, 6-(2-naphthyloxy) hexylacrylate, 8-(1-naphthyloxy) octyl acrylate, 8-(2-naphthyloxy) octylacrylate, and phenoxy ethyl acrylate.
 11. An article comprising: asubstrate; and an adhesive disposed on at least a portion of thesubstrate, the adhesive comprising: a (meth)acrylate-based copolymerhaving a refractive index of at least 1.48; particles of a thermoplasticpolymer, at least some of the particles having an average particle sizethat is larger than the wavelength of visible light, wherein therefractive index of the (meth)acrylate-based copolymer and thethermoplastic polymer particles are matched, and wherein the adhesivecomposition is optically transparent.
 12. The article of claim 11,wherein the adhesive composition is optically clear, having a visiblelight transmission of greater than 90%, and a haze of less than 5%. 13.The article of claim 11, wherein the substrate comprises a film, a tapebacking, a graphic article, a light guide, a plastic article, a wounddressing, a protection film or tape, a light extraction layer, a keypador membrane switch, a heat shrinkable layer, a display, a touch sensor,or substrate, or a moldable film.
 14. The article of claim 11, whereinthe particles of thermoplastic polymer comprise particles ofpolyethylene, ethylene vinyl acetate, ethylene methyl acrylate, ethyleneacrylic acid, ethylene acrylic acid ionomers, polypropylene, acrylicpolymers, polyphenylene ether, polyphenylene sulfide,acrylonitrile-butadiene-styrene copolymers, polyurethanes, and mixturesand blends thereof.
 15. The article of claim 11, wherein the(meth)acrylate-based copolymer comprises a copolymer of an aromaticmonomer in an amount of at least 5 parts per 100 parts of total monomer,the aromatic monomer having the formula:

wherein: Ar is an aromatic group which is an unsubstituted phenyl group,a substituted or unsubstituted fused or linked aromatic group, or asubstituted phenyl group substituted with a substituent selected fromthe group consisting of Br_(y) and (R³)_(z) wherein y represents thenumber of bromine substituents attached to the aromatic group and is aninteger from 0 to 3; R³ is a straight or branched alkyl of 2 to 12carbons; and z represents the number of R³ substituents attached to thearomatic ring and is an integer from 0 to 1, provided that both y and zare not zero; X is oxygen, sulfur or —NR⁴—, wherein R⁴ is H or C₁-C₄alkyl; n is 0 to 3; R¹ is an unsubstituted straight or branched alkyllinking group of 2 to 12 carbons; and R² is either H or CH₃.
 16. Thearticle of claim 11, wherein the adhesive is crosslinked.